bluewave

Probably one of the driest starts to October for the CONUS away from the Gulf area.

It goes beyond the seasonal guidance though. The first idea that we were going to make a run on +13 during December 2015 didn’t really happen until the month had already started. So the medium range guidance was way off also from late November. While that was an exceptional event around the Northeast, there were 10 other months since then for parts of the U.S. with a near +10 or greater departure. They also didn’t have much notice before the month started. This is how the seasonal guidance from the various models have been biased so cool. Any location that registers a +10 for at least one winter month is going to skew the whole winter departure well beyond what any of the seasonal models were indicating. That’s why even if the model gets the longitude of the ridge axis correct over the U.S., the temperature departures near the strongest part of the ridge have blown way past what the seasonal model forecasts were indicating. Near +10 or greater departure months in the U.S. since December 2015 Dec…2015….NYC….+13.3 JAN…2017….BTV…..+11.0 FEB….2017….ORD….+10.3 FEB…..2018…ATL….+10.6 FEB….2019…MGM….+10.5 JAN….2020…YAM….+9.8 DEC….2021….DFW….+13.2 JAN….2023….DXR….+12.3 FEB….2023…..SSI…..+9.8 DEC….2023….INL…..+15.8 FEB…..2024….FAR…..+17.5

The forecast at 500mb looks like a blend of 21-22 and Feb 18. So yes if that verified it would be a departure from the deep Western Trough of 22-23. That being said, none of these seasonal models have been great at this range so the finer details will have to wait.

The temps from the CanSIPS forecasts have been biased way too cold last few winters.

The 13-14 winter was one of what I call the big 5 of modern times. The other winters were 95-96, 09-10, 10-11 and 14-15. 95-96 still stands as the greatest winter in NYC Metro for wall to wall cold and snow from November into April. 09-10 was the greatest winter for snowfall from DC to Philly. 10-11 featured the greatest 33 day snowfall around NYC Metro at just over 60” from late December into late January. 13-14 was one of the best for snow combined with cold in the Great Lakes. 14-15 was tops for Boston snowfall. The 95-96 winter was before the big global temperature jump in 97-98. So NYC Metro was still able to register their snowiest winter with parts of Long Island recording over 90”. The extended cold from November into April hasn’t been rivaled either as the world has warmed. The next big global temperature rise to a new higher baseline occurred in 15-16 and no winters since then have been able to rival 09-10 in the mid-Atlantic. Same goes for 10-11 around NYC and 13-14 for the Great Lakes and 14-15 near Boston. Now we have seen one of the greatest global temperature rises over the last year or so. These big temperature rises make it unlikely that we could see one of these big 5 repeat again in this much warmer climate. So we can probably retire those 5 years as analogs for the new warmer climate.

I don’t think anyone is betting early on that this winter will rival the magnitude of the trough digging into the SW. That was the strongest trough out there of the last decade. But less trough in the SW doesn’t equal a great winter here absent other changes to the pattern.

Driest September on record for ISP and FRG. Time Series Summary for ISLIP-LI MACARTHUR AP, NY - Month of Sep Click column heading to sort ascending, click again to sort descending. 1 2024 0.24 0 2 2019 0.61 0 3 1985 0.81 0 4 1986 0.82 0 5 1965 1.01 0 6 1982 1.12 0 7 1980 1.28 0 8 2007 1.31 0 - 2005 1.31 0 9 1997 1.42 0 10 1976 1.49 0 Time Series Summary for FARMINGDALE REPUBLIC AP, NY - Month of Sep Click column heading to sort ascending, click again to sort descending. 1 2024 0.36 0 2 2019 0.50 3 3 2013 0.74 0 4 2007 1.34 0 5 2005 1.37 2 6 2022 1.76 0 7 2016 2.14 0 8 2017 2.19 0 9 2014 2.26 0 10 2001 2.32 0

The 22-23 winter was so warm in the East due to the Aleutian Ridge axis out near the Dateline coupled with the deep trough in the West. So this allowed the Greenland block based -AO to link up with the Southeast Ridge. While the WPO was positive, it didn’t have as much influence over the pattern for the East as other teleconnections. The 16-17 La Niña was very warm around NYC and the WPO was negative. 49-50 was the warmest La Niña winters of the older era and the WPO was negative also. So in the most general sense the 22-23 winter matched the winter pattern since 15-16 of an Aleutian Ridge and Southeast Ridge pattern. But it had an unusual combination of features not seen before in the same winter. I think all this talk of winters following exact past analogs is a bit of a misnomer. Since every new winter has combinations of features not seen before. This is where natural variability come in. So the current pattern since the summer has had some similarities to 2022. But to take that and say every feature going forward will be a carbon copy with no natural variability mixed in is misplaced. Plus exact magnitudes of winter warmth usually aren’t known until we at least see how the early winter verifies. Remember, none of the long range models as of November 2015 were forecasting a +13 December. The really big departures aren’t usually made known until we get into the short to medium range. 22-23 La Niña +WPO winter warm in the East 16-17 -WPO La Niña winter warm in the East 49-50 -WPO La Nina winter warm in the East

It’s based on the MJO RMM amplitude and VP anomalies in phase 5-6 during La Niña Octobers since 2010. The stronger October MJO responses had better winters in NYC relative to the other La Ninas in the multiyear event group. Those stronger MJO 5-6 Octobers also had the more robust peak La Niña ONIs from fall into winter of the multiyear groups. All the La Niña winters around NYC since 11-12 have averaged warmer than normal. But even the warmer than average 17-18 and 20-21 winters had better snowfall than the other years in the multiyear group. In addition, we haven’t had any cold neutral ENSOs in the -0.1 to -0.5 peak range with a strong -PDO since 2010. So not sure how the relationship would work for any year with the official CPC ONI not getting colder than -0.5. The other thing to consider is that we don’t know how long this relationship will continue to work it. So I will update this post with some early ideas for the coming winter after we see how the MJO verifies for the month of October. http://www.bom.gov.au/clim_data/IDCKGEM000/rmm.74toRealtime.txt https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php Multiyear La Niña groupings below with peak MJO 5-6 strength and the peak ONI from the fall into winter…….Strongest October MJO 5-6 and La Niña ONI leading to best NYC winters of the multiyear group bolded… October 2022…Phase 6 peak +2.177…..ONI….-1.0 October 2021….Phase 5 peak +2.087….ONI….-1.0 October 2020…Phase 5 peak +2.818….ONI…..-1.3 October 2017….Phase 6 peak +3.353….ONI….-1.0 October 2016….Phase 5 peak +1.800….ONI….-0.7 October 2011….Phase 6 peak +1.674….ONI….-1.1 October 2010….Phase 5 peak +2.880…ONI…..-1.6

That Aleutian Ridge from east of Japan to south of the Aleutians has been the most dominant 500mb height anomaly in the Northern Hemisphere since January.

Seems like the -PDO background 500mb and Pacific Jet pattern is continuing to be more impressive than the La Niña with a 600dm ridge east of Japan and 6 sigma jet max north of the Aleutians.

September will finish very close to average temperatures as the warm and cool departures canceled each other out. EWR….+0.5 NYC….-0.4 LGA….-1.3….strong flow off Sound kept LGA the coolest JFK…..+1.1…easterly flow from Nassau reduced the usual SW sea breeze HPN….+0.2 ISP…...-0.1 BDR….-0.9 New Brunswick…0.0 SMQ….+0.6 POU……+0.6

Only a 3° difference between the high and low in NYC today is the tied for the 2nd smallest for the month of September since 1943. TEMPERATURE (F) TODAY MAXIMUM 63 1055 AM 88 1945 71 -8 63 MINIMUM 60 838 AM 42 1888 58 2 59 https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=139&network=NY_ASOS&zstation=NYC&v=smallest&month=sep&_r=t&dpi=100&_fmt=png

Not sure about that since the overall conditions back in early August weren’t nearly as favorable for tropical development as we saw this week. This was the first time since 1952 that we had 3 named storms form from 9-24 to 9-27. The favorable MJO window in early August was still meeting resistance from the unfavorable atmospheric conditions which were in place before they dramatically improved this week.

Yeah, this was one of the strongest easterly flow Septembers we have seen due to the record west based blocking. This pattern lead to the historic flooding with Helene along with the global record atmospheric moisture. It was one of the strongest hurricane phasing events since Sandy.

The Pacific heading into October is fairly close to 2022 with a strong Aleutian Ridge and Western US Ridge. But the NAO is more negative this time. We’ll have to see how the rest of the month goes since it’s tough to forecast the whole month based on an early snapshot.

Just enough light rain to wet the ground at only .01 as we are closer to the high today than your area.

Just got a few breaks of sun here as the high pressure over New England is slowing the progress of the moisture coming north.

We got Debby back in early August during the last favorable MJO interval, but Helene was much more intense this week. My guess is that the warming surface SSTs relative to the higher atmosphere allowed a more unstable storm environment. I was pointing this out back during the August lull that a storm getting into the Gulf had a chance of really taking off due to the record SSTs. Notice the SST warming pulse just prior to Helene in the Gulf like we saw with the entire Atlantic basin. There were comments back in early August how people were surprised that the favorable MJO interval back then didn’t lead to another major hurricane like Beryl.

If you look at the VP anomalies there was a short window of improvement over the Atlantic this week so the effect was probably more subtle combined with the warming SSTs increasing instability.

Was enough to for NYC to drop to 3rd driest and Newark down to 2nd place. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Sep Click column heading to sort ascending, click again to sort descending. 1 1884 0.21 0 2 1914 0.29 0 3 2024 0.36 4 4 1885 0.41 0 5 2005 0.48 0 6 1941 0.51 0 7 1895 0.62 0 8 1951 0.70 0 9 2019 0.95 0 10 1881 0.97 0 Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of Sep Click column heading to sort ascending, click again to sort descending. 1 1941 0.14 0 2 2024 0.15 3 3 2005 0.45 0 4 1951 0.95 0 5 1972 1.03 0 6 1948 1.14 0 - 1939 1.14 0 7 1931 1.19 0 8 1953 1.25 0 9 1964 1.30 0 10 1967 1.35 0

My guess is that the uptick in tropical activity is related to the Atlantic warming in the last few weeks. Notice how the Atlantic was the warmest early in the season for Beryl and then dropped during the lull through August. Could be related to the lapse rates improving as the upper atmosphere differential probably wasn’t as great and the stability dropped. So we have a shot at finishing the season over 100 ACE which would be closer to average. We also had a lull during August 2022 and then an increase in September like this year. That year featured Ian in the Gulf during September and this year Helene. Warming surface decreased the delta from the upper levels to surface allowing more development.

I think the reason the warm front was a little further south than forecast yesterday was due to the models underestimating the influence of the high pressure in New England.